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How High do Monarch Butterflies Fly During Fall Migration?
Contributed by Dr. Bill Calvert
the highest you've ever known monarchs to fly?
A. Glider pilots have reported monarchs flying as high as eleven
Q. Why do they fly at such high altitudes?
A. At increasingly higher altitudes wind speed increases rapidly.
So if the winds are going in the right direction, it pays monarchs to
Q. Why don't monarchs always fly that high?
A. The height monarchs fly depends on which way the wind is blowing.
When winds are from the south, monarchs fly very low. Or, if the winds
are strong enough, they don't fly at all. They wait patiently in low areas
with lots of trees (if available) for the winds to turn around. During
these times, they mysteriously accumulate. This is when they form their
gigantic roosts and people are dazzled by large curtains of hanging butterflies
at night and early morning.
When the winds turn around the story is very different. During a typical
morning with correct winds, monarchs will burst out of their roosts after
they have warmed themselves enough to fly. Remember they are cold blooded
creatures (poikilotherms in scientific lingo) and must depend on sunlight
(radiation) to warm their flight muscles. Once they leave the roost they
may fly to a point in full sun where they bask some more or they may search
for a morning thermal, and ride the rising air upward, twisting and turning
like a feather caught in the wind. For more information about wind and
they go as high as the clouds?
A. If they fly at 11,000 feet they could certainly be above some
clouds. Clouds help to spot monarchs. That is, you can see a monarch against
a cloud much more easily than you can see one in clear air. If you saw
a group of them against a cloud and knew the height at which clouds began
that day, you would at least know the upper limit for the group you were
Q. Do monarchs go higher than the naked eye can see?
A. If the thermals are strong they may rise until we can see them
no more. Normally a group of migrants consists of butterflies flying a
many levels. Some will be within 100 feet of the ground. Others will rise
so high that they disappear from binocular view.
Q. At what altitude do they disappear from view?
A. You could do a simple experiment to see how far a butterfly
is when it disappears from view. Find a dead monarch or make one from
orange colored cardboard. It has to be the same size and approximate color
as a real monarch. Attach it to a highway sign on a little used road or
a playground if there is a large one nearby. Walk away from the sign until
you can no longer see the monarch, and then measure the distance from
you to the sign. You may have to get a parent to drive to measure the
tens of a mile. Try the same thing with binoculars.
Q. How much of their migration time do monarchs spend high in the sky,
and how much time down where they can be seen?
A. It's hard to say with certainty, but monarchs seem to fly at
least 3/4 of a day, say from 8:30 to 5:30 during days with good winds.
Sometimes they will stay up until just about dark. In deserts they come
down much earlier, perhaps as early as noon. It's not known what brings
them down. But the opportunity to nectar and too much heat may be factors.
This! Journaling Questions
- At what
distance do monarchs disappear from view? Try the experiment Dr. Calvert
suggests and send us your results!
- If glider
pilots have seen monarchs flying 11,000 feet in the air, how high is
that in miles? In kilometers?
- If surface
winds were 20 mph and winds at 3000 feet were 40 mph blowing from the
northwest, and a monarch rode thermal up to 3000 feet, how far could
a monarch fly in a day?
Science Education Standards
The behavior of individual organisms is influenced by internal cues
(such as hunger) and by external cues (such as a change in the environment).
of an organism's internal environment involves sensing the internal environment
and changing physiological activities to keep conditions within range
required to survive. (5-8)
is one kind of response an organism can make to an internal or environmental
Weather changes from day to day and over the seasons. Weather can be described
by measurable quantities, such as temperature, wind direction and speed,
and precipitation. (K-4)
Compute fluently and make reasonable estimates.
Understand measurable attributes of objects and the units, systems, and
processes of measurement.
Solve problems that arise in mathematics and in other contexts.
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